He sought to leave on a flight out of John Wayne Airport in Irvine earlier this month

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Adam Dandach, 20, who is accused of trying to board a flight to Istanbul, Turkey, with a fake passport so he could allegedly join Islamic State of Iraq and Syria, or ISIS, rebels, pleaded not guilty Monday, July 21, 2014, to federal charges.

A Southern California man accused of trying to board a flight to Istanbul, Turkey, with a fake passport so he could allegedly join Islamic State of Iraq and Syria, or ISIS, rebels pleaded not guilty Monday to federal charges.

Adam Dandach, 20, of Orange, remained in custody without bail and is expected in federal court in Santa Ana on Aug. 25.

Dandach was arrested by FBI agents assigned to the Orange County Joint Terrorism Task Force on July 3. He sought to leave on a flight out of John Wayne Airport in Irvine.

According to federal court documents, he told investigators that "he was traveling to Syria for the purpose of pledging his allegiance to ISIS, a known terrorist organization, that he would assist ISIS with anything that ISIS asked him to do, and that he believed the killings of U.S. soldiers are justified killings."

ISIS is the al-Qaida splinter group leading Sunni militants in Iraq.

Dandach had applied for an expedited replacement passport in June, explaining in the application that he had accidentally thrown the original in the trash while cleaning.

Authorities said his mother actually hid the original passport in a closet to stop him from flying to the Middle East in December.

Dandach's attorney, Cuauhtemoc Ortega of the Federal Public Defender's Office, as well as Dandach's family members declined comment to NBC4 after Monday's hearing.